She said: "It seems that the FSA may have known that there was a problem at Freeza Meats well before this scandal broke. When were they alerted to the presence of this meat at the company and why didn't they conducts any tests earlier."

The 10 tonne shipment at Freeza Foods in Northern Ireland was seized by environmental health officers in September last year amid concerns over the labels.

The product was due to be sent to Silvercrest, the Irish meat processor at the centre of the horse meat scandal, but was put into quarantine instead.

In the wake of the horse meat scandal the Food Standards Agency last month tested for equine DNA. The results, which came back yesterday, showed it contained 80 per cent horse meat.

The meat was sourced from Poland by McAdam Food Services, a meat broker based in Ireland. The company also supplied a shipment of beef to Rangeland Foods in Ireland which was found to contain 75 per cent horse DNA.

The owner of company was yesterday co-operating with authorities. The company said he was unavailable for comment because of the ongoing investigation but Mr Coveney told Irish politicians yesterday: "We need to establish what he knew and when he knew it. He is being very co-operative."

Freeza Meats said it did not buy the meat but held it as a gesture of “goodwill” on behalf of another company. No traces of horse DNA have been found in samples taken from Freeza Meats frozen beefburgers.

Asda said the beefburgers had been withdrawn as a “precautionary measure” and stressed that no horse meat has been found in beefburgers supplied by Freeza meats.

A spokewoman for Sodexo said: “Freeza Meats has not been a supplier to Sodexo since March 2012. Sodexo is aware of the investigations by the FSAI and the FSA and subsequent reports in the media.

“We have contacted our nominated suppliers for beef burgers and have received assurances that the companies cited in the FSAI and FSA reports have not supplied any mainland UK Sodexo sites. Sodexo is continuing to monitor the situation.”

A spokeswoman for the Food Standards Agency said the contaminated meat was "not released into the food chain at any point."